Much interest is directed at the chemical structure of hydraulic fracturing (HF) additives and the frequency of their use in unconventional gas exploitation. We conducted a quantitative survey and structural classification of HF chemicals in the U.S. based on the House of Representatives (“Waxman”) report for the years 2005-2009 and the database FracFocus for the years 2011-2013. Out of over 800 reported substances, classification by functional groups yielded succinct chemical subclasses able to illustrate the frequency and rationale of their use. Water-based guar gum predominated over polyacrylamide/-acrylate as gelling agent, and borate over zirconium as crosslinker. Practically every operation relied on petroleum hydrocarbons as solvents and non-emulsifiers. Nonylphenols – known as persistent endocrine disruptors – potentially form as breakdown products of ethoxylated surfactants. Some organic esters appear to be designed to release carboxyl groups as delayed acids and complexing agents in the subsurface. Such deprotection reactions in highly saline water, alongside with strong oxidants as breakers, bear the danger of organohalide generation. Choline chloride and glutaraldehyde are increasingly used as “green” clay stabilizer and biocide. Otherwise the preference for HF chemicals changed little over time. Such a review can identify indicator substances for monitoring and provide a knowledge base to guide future investigations of subsurface transformations, toxicity assessments and for optimizing wastewater treatment

Investigation of domestic wells in the vicinity of tight gas exploitation in Lower Saxony